Re: The Extinction Challenge (fwd)

Robert J. Bradbury (
Mon, 2 Aug 1999 07:34:14 -0700 (PDT)

> John Clark <> wrote:

> An Alpha particle will kill or mutate any cell it hits, a rare neutrino that hits
> would be almost as deadly.

John, I'm almost certain this is incorrect. Radiation doses are moderated by virtually all intervening mass. The denser the mass the quicker the moderation. An alpha particle is a helium nucleus and gets moderated much quicker than other forms of radiation (because it is bigger and interacts more quickly).

Only a very small fraction of each cell is DNA and 90+% of that is junk. So the probability that a alpha particle will kill or mutate a cell, is I believe very low.

I will grant that an alpha particle traveling at 99.999999% the speed of light is going to pack a pretty big punch and in this case may be pretty dangerous.

So I believe the *real* questions here is what is the effective energy (in MeV or J), and/or what is the absorption cross sectional area of the particle.

For absorption cross sectional area, I think:

Neutrino < Gamma-Ray < X-Ray < UV < Beta-particle < Alpha-particle.

The energy of the photon based radiations is directly calculatable, but the energy of the particles (and neutrinos???) depends on the nuclear reaction that generates them. [After all, weren't neutrinos invented to explain the mass that was "disappearing" from nuclear reactions?].